Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety and scope are covered structurally. The description adds one genuinely useful behavioral detail — that island nations yield an empty list rather than an error — but says nothing about ordering, disputed borders, or completeness of the result set.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences with no filler, with the core purpose front-loaded and the edge case second. The opening clause is slightly elliptical (missing a verb such as 'returns'), but nothing is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter lookup with an output schema and rich annotations, the description covers what the tool returns in substance plus the empty-result case. Only minor gaps remain, such as whether only contiguous land borders count.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, with both the localized country string and the locale enum fully documented in the schema. The description adds no meaning beyond that, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names the resource precisely — countries sharing a land border with a given country — which is distinct from sibling tools like get_country or compare_population. It does not explicitly name an alternative, so it stops short of full sibling differentiation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The domain makes the intended use obvious (fetch neighbours of one country), and the island-nation note hints at an edge case when there is no result. However, there is no explicit when-to-use/when-not guidance and no routing against alternatives such as get_country or search_countries.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.